Micro-Electro-Mechanical Systems, or MEMS can be defined as miniaturized mechanical and electro-mechanical systems where at least some elements have some mechanical functionality. Since MEMS devices are created with the same tools used to create integrated circuits, micromachines and microelectronics can be fabricated on the same piece of silicon to enable machines with intelligence.
MEMS structures can be applied to quickly and accurately detect very small changes in physical properties. For example, a microelectromechanical gyroscope can be applied to quickly and accurately detect very small angular displacements. Motion has six degrees of freedom: translations in three orthogonal directions and rotations around three orthogonal axes. The latter three may be measured by an angular rate sensor, also known as a gyroscope. MEMS gyroscopes use the Coriolis Effect to measure the angular rate. When a mass is moving in one direction and rotational angular velocity is applied, the mass experiences a force in orthogonal direction as a result of the Coriolis force. The resulting physical displacement caused by the Coriolis force may then be read from a capacitively or piezoresistively sensing structure.
In MEMS gyros the primary motion cannot be continuous rotation as in conventional ones due to a lack of adequate bearings. Instead, mechanical oscillation may be used as the primary motion. When an oscillating gyroscope is subjected to an angular motion orthogonal to the direction of the primary motion, an undulating Coriolis force results. This creates a secondary oscillation orthogonal to the primary motion and to the axis of the angular motion, and at the frequency of the primary oscillation. The amplitude of this coupled oscillation can be used as the measure of the angular rate.
A vibratory gyroscope operates on the principle of coupling of a primary mode vibration to a secondary mode vibration by Coriolis force induced by rotation of a body to which the gyroscope is attached. The operation of the gyroscope is strongly dependent on how the resonant frequency of the resonator for the primary mode vibration (primary frequency) and the resonant frequency of the resonator for the secondary mode vibration (secondary frequency) are selected in respect of each other. When the frequencies are far apart, the gyroscope is less sensitive to external vibrations and shows good stability over environmental changes e.g. temperature and time, but the detected amplitude is relatively low. The generated signal may be amplified electrically, but at the same time noise is amplified, so the signal-to-noise ratio tends to be very low. When the frequencies are closer, Coriolis movement is amplified by the gain of the secondary resonator, and better signal-to-noise ratio is achieved. However, at the same time, sensitivity to various external and internal factors increases. For many of these factors, sensitivity may be managed by added mechanical structures or electrical circuitry in the sensing device. However, such arrangements typically lead to added size and reduced robustness of the device.